1. Field of the Invention
The present invention relates to a fiber containing a large amount of inorganic fine powder, such as ultraviolet ray-shielding fiber or conductive fiber, and, in spite of its high content of the inorganic fine powder, having a fineness of not more than 8 deniers and being obtainable with stable spinning operation.
2. Description of the Prior Art
There has been used in recent years a process for providing fibers with various properties, which comprises kneading into a fiber-forming polymer an inorganic powder selected depending on the property to add, and then spinning the obtained composition into a fiber. For example, a white conductive fiber is obtained by kneading an inorganic powder of a white conductive metal oxide into a polymer and spinning the obtained composition. In another case, an inorganic powder of an ultraviolet ray-shielding inorganic powder is selected and kneaded into a fiber-forming polymer and the obtained composition is spun, to give an ultraviolet ray-shielding fiber. Further an inorganic powder of a specific pigment may be selected and kneaded into a fiber-forming polymer to give a composition, which is then spun into a spun-dyed fiber having a specific color.
It is however necessary in these fibers containing inorganic fine powder that the amount of the fine powder added be in a high level to produce the effect of the addition sufficiently. With, for example, white conductive fibers, an addition of a white conductive metal oxide in an amount below a specific level cannot connect the metal oxide particles linearly to produce conductive property. Likewise, too low an amount of an ultraviolet ray-shielding inorganic fine powder cannot produce a satisfactory ultraviolet ray-shielding effect. Such being the cases, there has been desired a technique that can add inorganic fine powders in large amounts.
In general, a large amount of inorganic fine powder incorporated into a polymer causes to rapid deterioration of the spinnability of the polymer. Furthermore, a large amount of inorganic powder exposed on the fiber surface scrapes away the surfaces of guides, rolls, drawing plates, travellers arranged in the fiber manufacturing equipment, thereby rendering it impossible to use these apparatuses any longer. Prolonged use of these surface-worn apparatuses will cause frequent fiber breakage and generation of many fluffs. Where a large amount of an inorganic powder is to be incorporated into a fiber, the inorganic powder should therefore be not present on the fiber surface. For this purpose one may figure out a process which comprises incorporating an inorganic powder into a polymer and producing a sheath-core composite fiber, while permitting the obtained polymer composition to constitute the core. In this case, however, it be6comes necessary to add still larger amount of inorganic powder to the core-component polymer, i.e. only part of the entire fiber, in order to produce a sufficient effect of addition for the entire fiber. Then, the still larger addition amount renders it more difficult to spin or thread the resulting core-component polymer composition stably.
To increase the spinnability of a core-component polymer containing a large amount of an inorganic powder, there is proposed use of thermoplastic elastomers as that polymer (Japanese Patent Application Laid-open No. 289118/1990). This technique comprises using as an inorganic fine powder a conductive metal oxide fine powder and as a core-component polymer a polystyrene-polyisoprene-polystyrene block copolymer, a polystyrene-polybutadiene-polystyrene block copolymer, polystyrene-polyisoprene block copolymer or hydrogenation products of the foregoing, whereby the core-component polymer containing a large amount of the conductive metal oxide powder exhibits good spinnability.
It is true that this technique can produce with no problem composite fibers with, however, a limitation that their finenesses should be at least 10 deniers. It is difficult with this technique to produce stably, in a high yield and with satisfactory quality, finer fibers with 8 deniers or below which is generally adopted as the fineness for fibers for clothing use. Besides, fibers containing a large amount of inorganic fine powder develop, when dyed, not so deep colors or bright colors, thereby failing to give finished fabrics having a color of high-grade feeling.